Singapore is a transit hub and Norwegian had no feeder traffic from there. SIA had numerous connections available and QF went onto Australia or had Jetstar for the SE Asia market. Norwegian competed against SQ, BA and QF for pax wanting direct flights and were slightly cheaper even after adding baggage a a couple of snacks, the problem was that you could fly full service for a similar fare if you took a connecting flight with the usual suspects and unless your origin/ destination was SIN/LHR you'd need a connection anyway.